The present invention relates to a method and an apparatus for adjusting the softening point of a pitch (hereinafter referred to as the “pitch material”) such as coal tar pitch or petroleum pitch.
When spinning carbon fibers from a pitch material, it is desirable that the pitch material have a high softening point to improve the spinning properties and smoothen post-spinning processing, such as when processing the spun pitch material to be infusible.
Japanese Laid-Open Patent Publication No. 9-143475 discloses an example of a method for adjusting the softening point of a pitch material. In this method, 500 g of a pitch material having a softening point of 125° C. is placed in a one-liter autoclave. Then, an oxidizing gas such as air is blown into the autoclave at a rate of five liters per minute while agitating and heating the pitch material at a temperature of 350° C. for two hours. This produces a pitch material having a softening point of 296.3° C.
However, the method described in the above publication requires an autoclave, which is a relatively costly apparatus, and a troublesome process of blowing oxidizing gas into the pitch material.